In a single-wafer thermal processing system, as one of a semiconductor manufacturing system, a semiconductor wafer (referred to simply as a wafer, hereinafter) is heated by lamps, and, thermal processing such as annealing, CVD, and oxidization processing are performed on the wafer. In this case, in order to heat the entire surface of the wafer uniformly, it is necessary to rotate the wafer with respect to the heating lamps. Such a type of system is disclosed by U.S. Pat. No. 5,755,511, for example. In this system, heating lamps are disposed above a processing chamber via a transmitting window, and also, an outer ring part outside of the processing chamber and an inter ring part inside of the processing chamber are coupled through a magnetic coupling at a bottom of the processing chamber, where the outer ring part and inner ring part are provided rotatably with respect to a fixed part of the processing chamber via bearing parts. The bearing parts include metal balls which directly come into contact with the outer ring part and inner ring part, respectively, and employ grease as a lubricant agent. Then, a driving part rotates the outer ring part, and the rotation force is transmitted to the inner ring part through the magnetic coupling. Thereby, a wafer placement part provided on the inner ring part is rotated.
In the above-mentioned system, as the grease is used as the lubricant agent in the bearing parts, the friction force is small. Accordingly, the inner ring part precisely follows the outer ring part rotating although the magnetic coupling has a small magnetic force. Thereby, the wafer on the wafer placement part stops in a predetermined orientation at high accuracy when the outer ring part is stopped. However, there is a possibility that vapor of the grease used in the bearing parts as the lubricant agent may contaminate the wafer. Further, as the inner ring part rotates on the rolling balls of the bearing parts, this type of bearing parts are not suitable for high-speed rotation.
Accordingly, the inventor of the present invention has been studying a ceramic bearing part not employing grease. However, as the ceramic bearing part has a friction force larger than that of a bearing part employing grease, when an outer ring part is stopped, an inner ring part stops in an orientation different from a predetermined orientation, that is, it stops in a condition in which a magnetic pole of the inner ring part is shifted in center from a magnetic pole of the outer ring part.
On the other hand, recently, in order to improve in-situ successive processing and throughput, a system called a cluster tool has been developed in which a plurality of thermal processing parts are connected to a conveying room including a conveying arm in an air-tight manner, and thermal processing is performed on a water successively therethrough. In the cluster tool, in order to perform a uniform process, the wafer is rotated by a placement table in some processing parts. In this case, a recess (depression) part which is an engagement part into which the wafer is fitted is formed in the placement table, and the wafer is rotated in a condition in which the wafer is fitted into the recess part.
Because the wafer has a orientation flat or V-shaped notch which is used as a mark for indicating an orientation of crystal. When an orientation in which the wafer is stopped from rotation in one thermal processing part is shifted from a predetermined orientation, the wafer is conveyed into a processing chamber of a subsequent thermal processing part in a condition in which the wafer is oriented in a wrong orientation. As a result, the wafer is not fitted into the recess part of the placement table of the subsequent processing part.
It is possible to attempt previously controlling a motor so as to compensate an expected shift/error in orientation of the wafer at the time of stopping of rotation. However, in such a method, when a friction torque is changed slightly with age, the stopping orientation is affected thereby. Accordingly, this method may not be practical.